This invention relates to television receivers and, more particularly, to digital receivers that are responsive to DPCM encoded signals.
The design of any receiver is of necessity tied to the design of the transmitter to which the receiver responds. This principles holds true in the design of HDTV receivers. To better understand the operation of a receiver, therefore, it is helpful to describe the encoding performed in the transmitter, because the necessary decoding that is carried out in the receiver is, then, self evident.
The prior art contains a number of television signal encoders that basically employ differential pulse code modulation (DPCM) encoding. By way of example, U.S. Pat. No. 4,794,455 issued Dec. 27, 1988 to S. Ericsson, describes a method and encoding apparatus employing adaptive filtering. It is one of many encoders where an encoding loop is used. The loop comprises a subtracter for removing from an applied signal an estimate signal, compressor to encode the difference signal applied to the compressor, a reconstructor to recover the difference signal, and an inner loop. The inner loop comprises an adder to add the previously removed estimate signal, a frame buffer, a motion compensator, and adaptive filtering to form the estimate signal. A receiver for such a transmitter must duplicate the reconstructor and the transmitter's inner loop. The adaptive filtering that forms the estimate signal. The motion compensation within the receiver must be identical to that of the transmitter, and the adaptive filtering within the receiver must be identical to that of the transmitter.
It makes sense, therefore, in reviewing the prior art of HDTV receivers, to review the prior art for HDTV transmitters.
A review of the prior art reveals, however, that the quantizers serving the function of the compressor in the Erricson patent are either completely fixed and linear, fixed and non-linear, or somewhat adaptive to the signal. Non explicitly attempt to force the output bit rate to a given rate. Also, all of prior art motion compensators translate fixed sized blocks of images, and no advantage is taken of the fact that certain image characteristics might permit larger block sizes in certain regions of the encoded image. Further, none of the prior art inner loops employ a leak factor that is sensitive to the nature of signal being encoded. All this is discussed in the Background of the Invention sections of the aforementioned applications. It is an object of this invention to create the receiver that comports with an HDTV transmitter design which overcomes the above mentioned deficiencies of prior art encoders.